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Accurately calculating speed from heavy truck skid marks can be difficult. As indicated in SAE article 910126“̈-.an accurate deceleration rate is often an elusive piece of the puzzle.” This paper is intended to add to work done by others in determining heavy truck deceleration rates and calculating speed from skid marks by using different deceleration rates through different portions of each skid length. Deceleration rates and skid lengths obtained from a test by the Washington Association of Technical Accident Investigators (WATAI)[2] will be used as a basis for an evaluation of the adjusted drag factor method for speed determination. The method is then used to compute truck speeds in a case in which a heavy truck left non-uniform skids of different lengths while braking and evasively steering.